24 THE RtCE WORM (tYLENCHUS ANGUSTUS) AND ITS CONTROL 



necessary to allow an attack of ufra to develop. The stand of paddy in the 

 " dry " plot was never strong and this may have helped to prevent an attack by 

 keeping the air humidity in the plot at too low a level to allow of free migration. 

 .•}-2-'17, cut all the stubble in the " wet " plot and its control, discarding the " dry " 

 plot and its control from further experiment. The stubltle from the " wet " infected 

 plot was stored in bags in the laboratory, while that from the ef)ntrol was burnt. 

 The plots were then ploughed up. 2-4-' 17, sowed local paddy .seed in a seed b<Hl. 

 5-7-' 17, transplanted this into the " wet " plot and its control. 31-7-'17, returned 

 the stubblc! that had been preserved in bags to the control plot, leaving the other 

 untouched. No ufra developed in either plot, the plants heading out normally 

 and giving a heavy yield in December. When the stubble was removed from the 

 bags for use in inoculating, it was found to have rotted badly and to be powdery 

 and damp. A number of the diseased ears were examined microscopically, and 

 though they contained plenty of dead worms not a single living one could be 

 found. The method of storage had obviously killed them, but the experiment 

 at lea.st confirmed the efficacy of removing the stubble and early ploughing in 

 checking infection from the previous crop. 



XI. The isolated plots at Dacca referred to as Experiment VIIT were sown with seed 

 taken from an infected field in 1917. Ufra developed towards the end of the rains 

 and destroyed about a quarter of the crop. 



The above experiments bring out certain points very clearly. No matter 

 when the worms reach the field, ufra only develops in the monsoon unless the 

 plants are kept covered so that they grow in a saturated atmosphere. When 

 covered, an attack can be induced even in the cold, dry part of the year 

 (Expts. IV and V), or later when it is still drier and very hot (Expt, VI). The 

 attack is readily induced by leaving infected stubble from a previous crop on 

 the field (Expts. VII and X), or by adding infected shoots to the water 

 (Expts. II, IX and X). It the stubble be carefully hand-picked ofE or the 

 infected crop burnt on the field, a perfectly healthy crop of paddy may be grown 

 in soil that bore a severely diseased crop the previous year (Expts. VII to X). 

 If the paddy is grown under " dry " conditions, an attack may be avoided even 

 where there is infected stubble from a previous crop in the field (Expt. X), 

 but the stand is poor and this may help to keep the air in the crop too dry to 

 allow of migration even in the monsoon. In any case paddy cannot be success- 

 fully grown under such conditions. Infective matter does not remain in the 

 soil if all the stubble be removed (Expts, VII and X), even though it can 

 scarcely be doubtful that the worms have, to some extent, been set free in the 

 soil by decomposition of fallen pieces of stubble. Infection may be carried 

 by the seed under certain conditions, provided that (as must often happen) 

 the seed is from a diseased crop and contains infected grains and empty florets 

 (Expts. VI and XI). 



As these last two points are of exceeding importance when considering 

 methods of checking the disease, they may be further examined. 



